The present invention relates generally to an improved method and system for fracturing a subterranean formation to stimulate the production of desired fluids therefrom.
Hydraulic fracturing is often utilized to stimulate the production of hydrocarbons from subterranean formations penetrated by wellbores. Typically, in performing hydraulic fracturing treatments, the well casing, where present, such as in vertical sections of wells adjacent the formation to be treated, is perforated. Where only one portion of a formation is to be fractured as a separate stage, it is isolated from the other perforated portions of the formation using conventional packers or the like, and a fracturing fluid is pumped into the wellbore through the perforations in the well casing and into the isolated portion of the formation to be stimulated at a rate and pressure such that fractures are formed and extended in the formation. Propping agent may be suspended in the fracturing fluid which is deposited in the fractures. The propping agent functions to prevent the fractures from closing, thereby providing conductive channels in the formation through which produced fluids can readily flow to the wellbore. In certain formations, this process is repeated in order to thoroughly populate multiple formation zones or the entire formation with fractures.
Wellbores having horizontal or highly inclined portions present a unique set of problems for fracturing. For instance, in many horizontal or highly inclined wellbores sections the wellbore has no casing or the annulus between the pipe and formation may not be filled with cement. In such completions, it may be difficult or impossible to effectively isolate portions of the formation in order to effectively fracture the formation. In other cases where solid pipe has been used in the horizontal or highly inclined wellbore section, fluid may exit the solid pipe section to a non-cemented annulus. In such situations, control of fracture placement or the number of fractures may be difficult.
Even with cemented casings, these typical techniques are not without problems. Fracturing certain formations may require multiple repositioning and multiple placement of conventional packers and fracturing equipment to properly fracture the entire formation. Such activities often result in delay, and therefore additional expense, as downhole equipment is repositioned and the formation repeatedly fractured. In addition, each time packers are repositioned, there are risks that packers may unseat or leak, possibly resulting in unsuccessful fracture treatment, tool damage, and loss of well control. Further, it may be desirable to fracture the entire formation in a single operation, for instance to reduce costs. In addition, when horizontal sections of wells are fractured, there is usually a tendency for most of the created fractures to be concentrated at areas that are weaker or may have been mechanically damaged during the drilling process. Quite often, such concentrated fracturing occurs near the turn in the well from the vertical to the horizontal section. In some instances, concentrated fracturing may be located near naturally-occurring weak zones due to the non-homogeneous nature of many reservoir rocks. This may result in inadequate stimulation of the well due to failure to fracture along the entire formation and may greatly reduce overall well production compared to the potential production had the producing zones of the formation been more completely fracture-stimulated.